The use of formed trays and peelable lids for those trays, has been known for some time. For example, food products such as microwaveable meals are commonly packaged in packages requiring a peelable lid. These packages are usually subjected to relatively severe processing conditions either at the point where the package is being filled and sealed or at the point where the package and its contents are to be used. In the packaging of food products, it is also desirable to provide lidstock material which will not only protect the food product from outside contaminants but is easily and readily peelable in order to provide the consumer with easy access to the product.
A particular problem is encountered in providing packaging for the severe process conditions of, for example, retort processing or the end use environments, in that there are only a limited number of packaging materials which can be used to provide the combined properties of (i) barrier functions, (ii) the ability to survive the severe processing and use conditions, (iii) safety for use in the packaging of food, and (iv) holding the package closed and containing the product.
Of special concern is providing a heat sealable film structure which forms the lid of the package, especially a retortable package, and which can be heat sealed to, for example, the peripheral flange of the tray and subsequently be removed with a moderate amount of force. The lid cannot, however, be so loosely sealed to the tray that it is inadvertently or otherwise undesirably released from the tray prior to an intentional opening of the package. Thus there is the requirement that the package seal tightly when closed but be readily openable. The closure must provide the necessary protection from the outside environment while the package is intended to be closed. The package should be capable of being opened with a moderate amount of force with a smooth and constant pulling. The removal of the lid should be smooth and steady when a constant opening force is applied, such that jerky motions or sudden releases of adhesion are not encountered.
Many sealant film structures which have utility in retort packaging are known. U.S. Pat. No. 5,407,751 is one exemplification of this art. However, while the art discloses sealant film structures useful in retort packaging, there still exists a need in retort packaging for a sealant film structure which not only meets the high demands of retort packaging but has a lower peel force.
The applicant has discovered a sealant film structure which meets the high demands of retort packaging while lowering the peel force necessary to remove said sealant film structure from the package.